Single-step pyrolytic synthesis of ultra-microporous ammonialized biochar for carbon dioxide capture

Carbon dioxide (CO₂) is a significant greenhouse gas that plays a pivotal role in driving global warming and climate change. Its primary sources stem from human activities, notably transportation, power generation, and industrial processes. Directly capturing CO₂ emissions at their origins is widely recognized as a potent and efficient approach to reducing emissions. Biochar has emerged as a promising material for capturing CO₂ owing to its stability, hydrophobic nature, ease of preparation, and economic advantages. Nevertheless, its ability to adsorb CO₂ is constrained in environments with relatively low pressure (<1 bar). Consequently, modifying and refining biochar is a strategy to enhance its affinity for CO₂. In this work, Leucaena leucocephala, a major invasive species in Asia, was selected as the biomass precursor, and a single synthesis process combining pyrolysis and ammonialization was employed to produce the ammonialized biochar (ABC). Among the synthesized biochars, ABC800 (produced at 800 °C) exhibits desirable surface properties with high surface area (S_BET = 836.5 m²/g), microporosity (S_micro = 753.3 m²/g), and ultra-microporosity (S_ultra-micro = 376.9 m²/g). In addition, ABC800 demonstrates superior CO₂ adsorption capacity (4.06 mmol/g at 0 °C). Isothermal and kinetic results show that ABC800's CO₂ adsorption follows the Langmuir-Freundlich and pseudo-second-order (PSO) equations, indicating both physical and chemical interactions. The correlation between adsorption performance, pore structure, and nitrogen content highlights the potential of ABC800 for CO₂ capture, particularly at elevated temperatures. Overall, this work offers new insights into a potentially sustainable approach for mitigating greenhouse gas emissions.